The present invention is directed to electric toothbrushes, and, more particularly, to a replacement head for an electric toothbrush having an electromagnetic drive unit.
One method for actuating the bristles, or other cleaning elements, of an electric toothbrush is an electromagnetic drive positioned within the handle portion of the toothbrush. The electromagnet can be actuated by a switch to oscillate at an operating frequency. A movable permanent magnet is positioned proximate to the electromagnet, such that the permanent magnet is driven to oscillate at an oscillating frequency by the electromagnet when the electromagnet is actuated. An elongated neck including a brush head is typically attached to the permanent magnet, such that the brush head is driven to oscillate by the movement of the permanent magnet.
Recognizing the need to replace toothbrush bristles after they are worn out, manufacturers have designed replacement heads that fit onto separate electromagnetic drive units. The drive units typically include the power source, switch, and electromagnet, and the replacement heads typically include the permanent magnet and the brush head. The replacement heads can be removably attached to the drive units, for instance, by threading a portion of the replacement head onto a portion of the drive unit.
More recently, manufacturers have attempted to control the movement of the brush head and cleaning elements of electric toothbrushes, in order to provide a more desirable cleaning motion, such as rotational motion about the central longitudinal axis of the toothbrush. Difficulties arise in doing so, especially in the case of toothbrushes with electromagnetic drives, because the generally linear oscillation of the permanent magnets in the replacement head must be converted into the desired rotational motion. One replacement head for an electromagnetic drive toothbrush that converts linear drive motion into rotational motion of the brush head is disclosed in U.S. Pat. No. 7,067,945 to Grez. However, the replacement head disclosed by the Grez patent may add difficulty in manufacturing, because it requires spring members within the brush head that must each be tuned to a particular size and shape so that they twist when oscillated at a preselected frequency.